EFFECTS OF COAGULATION MEDIUM ON ASYMMETRIC POLYETHERSULFONE MEMBRANE FOR CABON DIOXIDE AND METHANE SEPARATION JESSICO BIN MUTUN

Transcription

1 i EFFECTS OF COAGULATION MEDIUM ON ASYMMETRIC POLYETHERSULFONE MEMBRANE FOR CABON DIOXIDE AND METHANE SEPARATION JESSICO BIN MUTUN A thesis submitted in fulfillment of the requirements for the award of degree of Bachelor of Chemical Engineering (Gas Technology) FACULTY OF CHEMICAL & NATURAL RESOURCES ENGINEERING UNIVERSITI MALAYSIA PAHANG DECEMBER 2010

2 v ABSTRACT This study is concentrated on the ability and the performance of the asymmetric polyethersulfone membrane in gas separation process. Asymmetric flat sheet membranes were prepared by using a simple dry/wet phase inversion method. Experimental investigations were conducted focusing on the effect of the different coagulation medium during the phase inversion toward the permeability and the selectivity of the membrane to the carbon dioxide and methane gases. Three different coagulants medium were used which were water, methanol and water/methanol (50:50). The flats sheet asymmetric membrane then being characterized by using the scanning electron microscopy (SEM) and the Fourier transform infrared spectroscopic (FTIR). Gas permeation tests then run to examine the effect of the different coagulants toward the time of the gases pass through the membrane. From the result of the gas permeability unit calculation, membrane which immersed in water solution has shown the highest permeability. Different coagulant medium will affect the performance of the membrane toward its permeability and selectivity of gases. The water medium solution is the best coagulation medium for the asymmetric polyethersulfone membrane during the phase inversion method with the GPU value of As for the conclusion, water is identified as the best coagulation medium for asymmetric polyethersulfone membrane.

3 vi ABSTRAK Kajian ini tertumpu kepada kebolehan dan prestasi membrane poliethersulfone asimetrik dalam proses pengasingan gas. Membrane asimetrik datar lembar disediakan melalui proses pegeringan dan pembasahan. Kajian dijalankan memfokuskan tentang kesan-kesan koagulasi medium yang berbeza-beza terhadap ketelapan dan selektivitas karbon dioksida dan gas metana. Tiga jenis koagulasi medium yang berbeza digunakan iaitu air, metanol, dan campuran air/metanol (50:50). Membrane asimetrik datar lembar kemudiannya ditandakan mengunakan scanning electron microscopy (SEM) dan fourier transform infrared spectroscopic (FTIR). Perngujian ketelapan gas kemudianya dijalankan untuk megetahui kesan koagulasi medium yang berbeza terhadap masa yang melalui membrane. Daripada keputusan pengiraan unit ketelapan gas, membrane yang direndam ke dalam air menunjukkan ketelapan yang tertinggi. Koagulasi medium yang berbeza akan mempengaruhi prestasi ketelapan dan selektivitas membrane tehadap gas-gas yang diuji. Air merupakan koagulasi medium yang terbaik untuk membrane poliethersulfone asimetrik semasa proses fasa inversi dengan nilai GPU ialah Konklusinya, air telah dikenalpasti sebagai koagulasi medium terbaik untuk membrane poliethersulfone asimetrik.

4 vii TABLE OF CONTENTS CHAPTER TITLE PAGE DECLARATION ii DEDICATION iii ACKNOWLEDGEMENT iv ABSTRACT v ABSTRAK vi TABLE OF CONTENTS vii LIST OF TABLES xi LIST OF FIGURES xiii LIST OF EQUATION xv LIST OF SYMBOLS xvi LIST OF APPENDICES xviii

5 viii I INTRODUCTION Background of Study Problem Statement Objective of Study Scope of Research Rational and Significant 3 II LITERATURE REVIEW History of Membrane Membrane Classifications Membrane Modules Membrane Applications Gas Membrane Separation Advantages of Membrane Gas Separation Asymmetric Membrane Formation 19

6 ix 2.8 Dry/Wet Phase Inversion Process Polyethersulfone Polymer Polymeric Dope Solution 22 III METHODOLOGY Introduction Experimental Procedures Polymeric Dope Solution Preparation Membrane Casting Membrane Coating SEM and FTIR Gas Permeation Test 31

7 x IV RESULT AND DISCUSSION Morphology of Asymmetric PES Membranes Gas Permeation Test Result 37 V CONCLUSION AND RECOMMENDATIONS Conclusion Recommendation 45 REFERENCES 46

8 xi LIST OF TABLE TABLE NO TITLE PAGE 2.1 Membrane Type and Characteristic Configuration of Membrane Module Materials for Gas Separating Membrane Gas Separation and Its Application Basic Properties of Water and DMAc Basic Properties of PES Basic Properties of Water, and Methanol for Coagulation Medium Result of Permeation Test of CO 2 at 1 bar on membranes immersed in different coagulation medium Result of Permeation Test of CH 4 at 1 bar on membranes immersed in different coagulation medium 39

9 xii 4.3 Permeation Properties of Asymmetric PES membrane immersed in water Permeation Properties of Asymmetric PES membrane immersed in Methanol medium solution Permeation Properties of Asymmetric PES membrane immersed in water/methanol medium solution 40

10 xiii LIST OF FIGURES FIGURE NO TITLE PAGE 2.1 Membrane Classification General Membrane Process Schematic Diagram of the Basic Membrane Gas Separation Process Asymmetric Membrane Structure Repeating Chemical Structural of PES General steps of study of effects of asymmetric polyethersulfone membrane on different coagulation medium Dope Solution Preparation System Asymmetric Membrane with Silicone Coating Gas Permeation System Scanning electron photomicrograph of flat sheet

11 xiv asymmetric PES membrane at magnification of Surface layer of coated membrane micrographs at different coagulation medium at 100X magnification The normalized difference spectrum of asymmetric PES membrane Comparison between the means selectivity on each membranes that immersed in different coagulation medium Permeability of CO 2 in water, methanol, and water methanol medium solution Permeability of CH 4 in water, methanol, and water/methanol medium solution 42

12 xv LIST OF EQUATION EQUATION NO TITLE PAGE 2.1 Fick s Law Solution-Diffusion Pressure-Normalized Flux Gas Permeation Unit Pure Gas Selectivity 16

13 xvi LIST OF SYMBOLS ABBREVATIONS PES - Polyethersulfone polymer DMAc - N, N Dimethylacetamide CO 2 - Carbon dioxide CH 4 - Methane GPU - Gas Permeation Unit C 2 H 6 - Ethane CO - Carbon monoxide N 2 - Nitrogen H 2 - Helium

14 xvii PARAMETERS/SYMBOL J - Membrane flux k - Solubility of gas in Membrane D - Diffusion Coeffient of Gas Through Membrane p - Partial Pressure Different l - Membrane thicknes Q i/j - Volumetric flow rate of gas in standard temperature and Pressure A - Membrane active surface area α i/j - Pure gas selectivity

15 xviii LIST OF APPENDICES APPENDIX TITLE PAGE A Gas Permeation Unit Calculation 48

16 1 CHAPTER 1 INTRODUCTION 1.1 Background of Study A separation process is used to separate a mixture to two or more difference products. The separation processes deal mainly with the transfer and change of energy and the transfer and change of materials, primarily by physical means but also by physical-chemical means (Christie, 2003). Separation process can be classified into process like evaporation, distillation, absorption, adsorption, membrane separation, mechanical-physical separations, and many more. Uses of membrane have been rapidly growing in the application of gas separation process. This study is concentrated on the ability and the performance of the membrane to separate the carbon dioxide (CO 2 ) from methane (CH 4 ). It is because in the gas stream, CO 2 which fall into category of acid gases (as does

17 2 hydrogen sulfide (H 2 S)) will bring harm to the equipment and the pipeline itself because with the combination with water, it is highly corrosive and rapidly destroy pipeline and equipment. Membranes have been widely used in two main CO 2 removal applications which are in natural gas sweetening, and enhanced oil recovery, where CO 2 is removed from an associated natural gas stream and reinjected into the oil well to enhanced oil recovery (David, 1999) 1.2 Problem Statement In membrane separation the most important part is the permeability and selectivity of the membrane toward the gases that need to be removed to get better separation result. This study is performed to study and review the selectivity and permeability of the membrane which immersed into three different coagulations medium. Beside that the structures of each membrane need to be viewed and characterized by using the Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopic (FTIR). It is important to know what the best coagulation medium for PES asymmetric membrane is in order to get the best performance of the membrane. Ideal asymmetric membranes for gas separation must meet the following requirements for better performance. First is the skin layer must be defect free to assure that the permeation is exclusively controlled by a solution/diffusion mechanism to achieve maximum selectivity. Secondly is the skin layer should be as thin as possible to maximize the membrane productivity. Thirdly is to the substructure should provide sufficient mechanical strength to support the delicate skin layer during high-pressure operation.

18 3 1.3 Objective of Study The main objective of this study is to investigate the effect of coagulation medium towards the permeability and selectivity of the membrane for the separation of the CO 2 and CH Scope of Research Based on the objective, this study mainly conducted to develop membrane for gas separation by study the effect of the different coagulation medium toward the membrane. To achieve the objective of the study, few scopes of study are conducted as below: i. Fabrication of membrane for gas separation base on asymmetric flat sheet membrane. ii. Various permeability tests conducted for CO 2 and CH 4. iii. Membrane characterized by using SEM and FTIR. 1.5 Rationale and Significant Lots of fact and information in gas separation process using membrane can be studied by doing this project. Furthermore, by doing the analysis of the gas permeation, the selectivity and permeability of the membrane can be further review and studied to get better result of gas separation. Besides that, this opportunity can

19 4 be used to learn how to fabricate and preparing the asymmetric flat sheet membrane to separate gases.

20 5 CHAPTER 2 LITERATURE REVIEW 2.1 History of Membrane A membrane can be defined as semi-permeable barrier, which separates a fluid and restricts transport of various chemicals in selective manner. A membrane can be homogenous or heterogeneous, symmetric or asymmetric in structure, solid or liquid, can carry a positive or negative charge or be neutral or bipolar (Srikant, 2008). Transport trough a membrane can be affected by convection or by diffusion of individual molecules, induced by an electric field or concentration, pressure or temperature gradient. The membrane thickness may vary from as small as 100 microns to several millimeters (mm). The membrane studies already started in the early eighteenth century when Abbe Nolet used the word osmosis to describe permeation of water through a diaphragm in 1748 (Baker, 2004). Through the nineteenth and early twentieth century s,

21 6 membranes had no industrial or commercial uses, but were used as laboratory tools to develop physical and chemical theories. This can be proved with the measurements of solution osmotic pressure made with membranes by Traube and pfrffer were used by Van t Hoof in 1887 to develop his limit law, which explains the behavior of ideal dilute solution (Baker, 2004). The concept of a perfectly selective semipermeable membrane was used by Maxwell and others in developing the kinetic theory of gases. In 1907, Bechold devised a technique to prepare nitrocellulose membranes of graded pore size, which determined by bubble test. Others efforts by Elford, Zsigmondy and Bachmann and Ferry improved on the Bechold s technique and by the early 1930s microporous collodion membranes were commercially available. Then the next 20 years after that, the early microfiltration membrane technology was expanded to other polymers, notably cellulose acetate. The transformation of membrane separation from a laboratory to an industrial process came first in the 1960 with the development of the asymmetric porous membranes by Loeb and Sourirajan (Nutes, 2001). The membranes consist of an ultrathin, selective surface film on a much thicker but much more permeable microporous support, which provides the mechanical strength (Baker, 2004). The period from 1960 to 1980 produced a significant change in the status of membrane technology. Building the original Loeb-Sourirajan technique, other membrane formation processes, including interfacial polymerization and multilayer composite casting and coating, were developed for making high performance membranes. Using these processes, membranes with selective layers as thin as 0.1 μm or less are now being produced by a number of companies. Method of producing of membranes into large-membrane-area spiral-wound, hollow-fine-fiber, capillary, and plate and frame modules were also developed, and advances were made in improving membrane stability.

22 7 By 1980, microfiltration, ultrafiltration, reverse osmosis and electrodialysis were all established processes with large plants installed worldwide (Baker, 2004). Today, membranes are used on a large scale to produce portable water from sea and brackish water (desalination), to clean industrial effluents and recover valuable constituents, to concentrate, purify, or fractionate macromolecular mixtures in the food and drug industries, and in this project consideration which is to separate gases and vapors in petrochemical processes. 2.2 Membrane Classifications Membrane can be classified into few types and can be determined by the specific application objective which includes the particulate or dissolve solids removal, hardness reduction or ultra pure water production, removal of specific gases or chemical and many more. The classification of membrane can help to improve the membrane application by knowing to the membrane morphology. Membranes classified according to their morphology are shown in figure 2.1 and the details about the membrane types are discussed in table 2.1. Membrane Dense Porous Composite Symmetric Asymmetric Figure 2.1 Membrane classification Table 2.1: Membrane type and characteristics.

23 8 Membrane type Characteristics References Microporous membranes The membrane behaves almost like a fibre filter and separates by a sieving mechanism determined by the pore diameter and particle size. Materials such as ceramics, graphite, metal oxides, and polymers are used in making this type of membrane. The pores in the membrane may vary between 1 nm to 20 microns. Srikant, 2004 Homogeneous Membranes This is a dense film through which a mixture of molecules is transported by pressure, concentration or electrical potential gradient. Using these membranes, chemical species of similar size and diffusivity can be separated efficiently when their concentrations differ significantly. Srikant, 2004 Asymmetric membranes An asymmetric comprises a very thin (0.1 to 1.0 micron) skin layer on a highly porous ( microns) thick substructure. The thin skin acts as the selective membrane. Its separation characteristics are determined by the nature of membrane material or pores size, and the mass transport rate is determined mainly by the skin thickness. Porous sub-layer acts as a support for the thin, fragile skin and has little effect on the separation characteristics. Srikant, 2004 Nonporous, dense Nonporous, dense membranes consist of a dense film through which permeants are transported by Baker, 2004

24 9 membranes diffusion under the driving force of a pressure, concentration, or electrical potential gradient. The separation of mixture relate to the relative transport rate within membrane materials which is determined by the diffusivity and solubility in the membrane material. Most gas separation, pervaporation, and reverse osmosis membranes use dense membranes to perform the separation. Electrically charged Membranes Electrically charged membranes can be dense or microporous, but are most commonly very finely microporous, with the pore walls carrying fixed positively or negatively charged ions. A membrane with fixed positively charged ions is referred to as an anion-exchange membrane because it binds anions in the surrounding fluid. Similarly, a membrane containing fixed negatively charged ions is called a cationexchange membrane. Separation achieved mainly by exclusion of ions of the same charge as the fixed ions of the membrane structure, and to a much lesser extent by the pore size. The separation is affected by the charge and concentration of the ions in solution. Electrically charged membranes are used for processing electrolyte solutions in electrodialysis. Srikant, Baker, 2004 and

25 Membrane Modules Nowadays with the advance technology in membranes separation, the materials to form a membrane have been formulated to get the best separation result. For that reason, different types of membrane module are designed and available in the market. The configurations of membrane module have been discussed in table 2.2. According to Srikant, 2004, the following membrane modules are largely used for industrial applications: I. Plate and frame module II. Spiral wound module III. Tubular membrane module IV. Capillary membrane module V. Hollow fiber membrane module Table 2.2: Configuration of Membrane module (Philip, 1988) Membrane modules Details Hollow Fiber - Very small in diameter membrane (< 1mm) Capillary Consist large number of membranes in a module and self supporting Density is about 600 to 1200 m 2 /m 3 (for capillary membrane). Up to m 2 /m 3 (hollow fiber). Size is smaller than other module for given performance capacity. Process is inside-out. Permeate is collected outside of membrane. Plate and Frame Structure is simple and the membrane replacement is easy.

26 11 Similar to filter press Density is about 100 to 400 m 2 /m 3. Membrane is placed with feed sides facing each other. Feed flows from its sides and permeate comes out from the top and the bottom of the frame. Membranes are held apart by a corrugated spacer. Spiral Wound Formed from a plate and frame sheet wrapped around a center collection pipe. Density is about 300 to m 2 /m 3. Its diameter can up to 40cm. Feed flow axial on cylindrical module and permeate flow into the central pipe. Tubular Not self supporting and normally are inserted in other materials tube with diameter more than 10mm. Density is not more than 300 m 2 /m 3. Membranes replacement is easy. 2.4 Membrane Applications Membranes are becoming popular in separation process industries in recent day. There are various types of membrane separation have been developed the specific industrial applications. The following are the some of the widely used processes that use membrane.